The present invention relates to a solid electrolytic capacitor.
Solid electrolytic capacitors have superior high frequency characteristics and large capacities in addition to being compact. Thus, solid electrolytic capacitors are widely used in high frequency circuits of various types of electronic devices such as personal computers and imaging devices.
A typical method for manufacturing a solid electrolytic capacitor will now be discussed. First, powders of valve metals such as niobium (Nb) and tantalum (Ta) are pressurized and molded to form with an anode lead and then sintered to form a sintered body. The sintered body is then anodized to form a dielectric layer, which mainly includes oxides, on the surface of the sintered body. An electrolyte layer (e.g., conductive polymer layer of polypyrrole, polythiophene, and the like) is formed on the dielectric layer. A cathode layer (e.g., a laminated film of a conductive carbon layer and a silver paste layer) is formed on the electrolyte layer. In this manner, a capacitor element is obtained. The anode lead of the capacitor element is welded and connected to an anode terminal. The cathode layer of the capacitor element is connected to a cathode terminal by a conductive adhesive. Then, a transfer process is performed to mold and complete a solid electrolytic capacitor.
In the above-mentioned electronic device, the resistance components of solid electrolytic capacitors are required to be minimized. Research is being conducted to lower the equivalent series resistance (ESR) of a solid electrolytic capacitor (see e.g., Japanese Laid-Open Patent Publication No. 7-94368).
The '368 publication proposes mixing a powder, such as graphite powder, conductive polymer compound powder, or metal powder, to the conductive polymer layer of the solid electrolytic capacitor to form ridges and valleys in the surface of the conductive polymer layer. Such an irregular surface of the conductive polymer layer increases the mechanical adhesion force of the conductive polymer layer and the cathode layer (particularly, the conductive carbon layer in the cathode layer) and reduces the equivalent series resistance in a high frequency region.